In general, spun bond nonwoven production machines can be classified as eductive “open” spinning systems and non-eductive “closed” spinning systems. Conventional broad loom eductive systems can generally trace their roots to the subject matter disclosed in U.S. Pat. No. 3,802,817 (Matsuki et al.) which describes a system that extrudes a curtain of filaments, extending the full width of the machine into, atmosphere (and/or impinged with cooled air). The curtain is then subjected to the action of a pair of air jet streams in a sucker, or filament drawing unit, the jet velocity of said jet streams being selected in the turbulent range. The jets act to entrain air from atmosphere along with the fibers which are then projected from the drawing unit onto a gas pervious conveyor belt collector to form a web. The quenching air system is separate from the filament drawing unit system. The fibers being spun are typically exposed to atmosphere at least once and usually twice: once just after being extruded and then again between the drawing device and the collector belt. This basic design has evolved into modern systems, for example, see U.S. Pat. Nos. 6,183,684 (Lu), 6,783,722 (Taylor) and 6,692,601 (Najour), all of which describe improved non-eductive “open” spinning nonwoven production systems.
Conventional broad loom non-eductive spinning systems can generally trace their roots to the disclosure in U.S. Pat. No. 4,405,297 (Appel et al.) which describes a system for forming spun bond nonwoven webs by spinning a plurality of filaments into a quench chamber where they are contacted with a quenching fluid, then utilizing the quench fluid to draw the filaments through a nozzle spanning the full machine width, and collecting the filaments as a web on a gas pervious conveyor belt collector. The fibers being spun are usually enclosed or shielded from atmosphere until they are formed into a web on a conveyor. This basic design has evolved into modern systems, for example U.S. Pat. No. 5,032,329 (Reifenhauser).
There are also hybrids of the two arts in which closed systems are aided by high pressure eductive jets to increase filament speeds, as shown in U.S. Pat. Nos. 5,503,784 (Balk) and 5,814,349 (Geus et al.).
The systems and methods discussed above have various disadvantages and limitations. Specifically, eductive (open) type systems inherently create high levels of turbulence and vorticity that are hard to control from day to day, and which tend to entangle and group the filaments into bundles, thereby limiting the uniformity of the final products. Furthermore, prior art eductive systems involve small fixed eductor throat openings which suffer drawbacks such as frequent plugging and cannot be opened to clear drips and plugs. In addition to plugging the throat of an eductor, small deposits of polymer drippings, monomer build up and scratches from constant cleaning all affect the patterns of turbulence on a day to day, and even on an hour to hour basis. The high speed jet nozzles themselves tend to become clogged by debris that enter from the process air supply and monomer, thereby drastically upsetting flow in the highest speed areas and creating vortices in the drawing unit. These systems also require two sources of air and two sets of associated equipment; one, a low pressure cooled air source that is used to quench the molten filaments by removing heat energy; and the other, a high pressure air source required to produce high velocity air to draw the filaments. The high velocity air generates high noise levels as it draws the filaments. While higher spin speeds required for spinning polyester and Nylon can be achieved with specialized eductive systems, the problems of turbulence and system hygiene are amplified by higher air jet pressures and velocities. Thus, forming a uniform web is very difficult with these systems because the fiber/air stream is moving very fast relative to the vertically stationary (but horizontally moving) collector belt. The amount of energy in the stream is so high at the belt that the fibers tend to bounce off the belt. The fibers can also be blown off the belt by the excess of air that cannot be passed through the below-the-belt vacuum system that generally is not able to evacuate all of the process air.
Conventional non-eductive (closed) systems typically permit somewhat more web formation control than do eductive systems; however, the non-eductive systems have fiber spin speed limitations. The long nozzle or throat sections where the fibers are attenuated are subjected to large structural loads from pressurized quench fluid. Even at pressures slightly above atmosphere, these walls must sustain loads of thousands of kilograms. These pressure loads cause deflection of the walls which, in turn, have to be pushed back into place uniformly across the machine width. The geometry of the nozzle controls quench fluid speed, which in turn controls fiber speed and formation of the web. Structural support of the wall geometry severely limits the pressure of the quench fluid, ergo the permissible velocity of the fluid in the nozzle and fiber speed. Also, the large surface areas of the nozzle have the same system hygiene problems as are present in eductive systems, but there is more surface area for deposits to collect, and it is not easy to get inside these nozzles to effect cleaning.
Hybrid systems were conceived primarily to increase the spin speeds of non-eductive systems. Hybrids typically incorporate eductive air jets somewhere along the nozzle area, which act to boost nozzle velocity without increasing quench fluid pressure. These systems have worked for some but not all higher speed spinning applications, and tend to be very complicated and capital intensive, and require substantial operation and maintenance attention.